Three-phase four-bridge-arm inverter system based on stationary coordinate system control and control method thereof

Abstract

The application discloses a three-phase four-bridge-arm inverter system based on a stationary coordinate system control and a control method thereof, which comprises four parallel bridge arms, an auxiliary network and a control module. The auxiliary network comprises two series filter capacitors and a filter inductor connected to the midpoint of the two filter capacitors. The filter inductor is connected to the midpoint of the fourth bridge arm, and the two filter capacitors are connected in parallel with the four bridge arms. The control module comprises a first control module and a second control module. The first control module controls the first three bridge arms based on a phase voltage effective value ring, a phase voltage transient ring, an inductor current transient and a third harmonic injection ring. The second control module controls the fourth bridge arm based on the modulation of a third harmonic voltage, the modulation of a zero sequence current and the modulation wave of a three-phase output voltage. The first three bridge arms realize independent control to inhibit the influence of negative sequence, and the fourth bridge arm eliminates the influence of zero sequence. The system stability is improved, and the calculation amount and complexity of the control strategy are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the control of power electronic inverter power supply, in particular to a three-phase four-bridge-arm inverter system based on static coordinate system control and a control method thereof. BACKGROUND

[0002] In recent years, with the gradual increase in demand for the number of electric vehicles (EV), electric vehicles are used as energy storage systems to exchange energy with the power grid in both directions, such as vehicle-to-home (V2H) and vehicle-to-load (V2L) modes. With the increasing maturity and advancement of isolated AC-DC converter technology, electric vehicle chargers can not only charge the battery from the power grid to the vehicle, but also feed energy from the vehicle back to the power grid (V2G), or even form a power grid when the power grid infrastructure is missing, i.e. V2H and V2L, which means that electric vehicles are more like distributed energy storage units rather than just loads. It is feasible to use electric vehicles to support residential electricity.

[0003] The V2H function can provide power to the home when the power grid is out of service, providing a new way for efficient and flexible use of energy. However, household electrical equipment is complex and diverse, which can easily cause three-phase load imbalance. In order to solve this problem, there are currently three main solutions: the first is to add another switching bridge arm on the basis of the three pairs of bridge arms of the two-level three-phase inverter, and to control it using a three-dimensional space vector pulse width modulation (3D-SVM) algorithm, but this control algorithm is very complex, changing the number of space vectors of the three-phase inverter from 23 to 24, and the complexity and difficulty of the control algorithm increase greatly with the increase in the number of vectors; the second is to separate positive and negative sequences by symmetric component method, and then separate zero sequence by the fourth bridge arm, and to control the positive, negative and zero sequences separately, which requires a large number of mathematical operations, making the entire control system complex and difficult to implement, and requiring a high-performance control chip. The third method is to use split capacitor method, which requires a large split capacitor to maintain the midpoint balance, and has the disadvantages of high cost and large size. The midpoint voltage of the upper and lower split capacitors will only cause distortion of the output waveform if it is not balanced. Recently, there has also been a method of detecting zero sequence current, in which the neutral point of the load is connected to the fourth bridge arm through an inductive element. This method cannot balance the split capacitor midpoint voltage in extreme imbalance, and thus cannot guarantee the quality of the output waveform and the balance of the output three-phase voltage. In addition, due to the use of SPWM modulation, the DC utilization rate is relatively low. SUMMARY

[0004] The present application provides a three-phase four-bridge-arm inverter system based on static coordinate system control and a control method thereof, which can improve the stability of the system and reduce the computational complexity of the control strategy.

[0005] Technical solution: To solve the above problems, the application adopts a three-phase four-bridge-arm inverter system based on static coordinate system control, which comprises four parallel bridge arms, an auxiliary network, an output side filter and a control module, the auxiliary network comprises two series DC voltage division filter capacitors and a filter inductor L connected to the midpoint N of the two DC voltage division filter capacitors n , the filter inductor L n is connected to the midpoint of the fourth bridge arm, the two series DC voltage division filter capacitors are connected in parallel with the four bridge arms, the midpoint N of the two DC voltage division filter capacitors is connected to the output side filter, the midpoints of the first, second and third bridge arms are connected to the output side filter, the control module comprises a first control module and a second control module, the first control module controls the first, second and third bridge arms based on the phase voltage effective value ring, the phase voltage transient ring, the inductor current transient and the injected third harmonic ring, and the second control module controls the fourth bridge arm based on the modulation of the third harmonic voltage, the modulation of the zero sequence current and the modulation wave obtained by adding the three-phase output voltage values.

[0006] Further, the first bridge arm comprises power switch tube T1 and power switch tube T2, the second bridge arm comprises power switch tube T3 and power switch tube T4, the third bridge arm comprises power switch tube T5 and power switch tube T6, the fourth bridge arm comprises power switch tube T7 and power switch tube T8, the output side filter comprises filter inductor L a , filter inductor L b , filter inductor L c , filter capacitor C a , filter capacitor C b and filter capacitor C c , one end of filter inductor L a is connected to the midpoint of power switch tube T1 and power switch tube T2, the other end of filter inductor L a is connected to filter capacitor C a and A phase load; one end of filter inductor L c is connected to power switch tube T3 and power switch tube T4, the other end of filter inductor L c is connected to filter capacitor C b and B phase load; one end of filter inductor L c is connected to power switch tube T5 and power switch tube T6, the other end of filter inductor L c is connected to filter capacitor C c and C phase load, filter capacitor C a , filter capacitor C b and filter capacitor C c are all connected to the midpoint N of the two DC voltage division filter capacitors, and A phase load, B phase load and C phase load are also connected to the midpoint N of the two DC voltage division filter capacitors.

[0007] Further, the first control module comprises a first PI controller, a first PR controller, a second PI controller and a first PWM generator, the input of the first PI controller is the difference between the effective reference value of phase voltage and the effective value of phase output voltage, the input of the first PR controller is the difference between the reference value of phase transient voltage loop and phase output voltage, the output of the first PR controller is the reference value of transient current loop, the reference value of phase transient voltage loop is obtained by multiplying the output value of the first PI controller with the reference sine, the input of the second PI controller is the difference between the reference value of transient current loop and phase output inductance current, the input of the first PWM generator is the output of the second PI controller plus the injected third harmonic, and the PWM wave output by the first PWM generator is used for the control of the first bridge arm, the second bridge arm or the third bridge arm.

[0008] Further, the second control module comprises a second PR controller, a third PR controller, a fourth PR controller and a second PWM generator, the input of the second PR controller is the difference between the average value of three-phase output voltage and 0, the input of the third PR controller is the difference between the voltage of the midpoint N and the third harmonic, the input of the fourth PR controller is the difference between the zero sequence current and the current of the filter inductance L n multiplied by the impedance of the auxiliary network, the input of the second PWM generator is the sum of the output values of the second PR controller, the third PR controller and the fourth PR controller, and the PWM wave output by the second PWM generator is used for the control of the fourth bridge arm.

[0009] Further, the DC conversion module in parallel with the four bridge arms is a Boost DC converter, a non-controlled rectifier or a battery pack.

[0010] The application also adopts a control method of a three-phase four-bridge-arm inverter system based on static coordinate system control, which comprises individual control of the four bridge arms, control of the first bridge arm, the second bridge arm and the third bridge arm based on phase voltage effective value loop, phase voltage transient loop and current transient loop, and control of the fourth bridge arm based on the modulation of the third harmonic, the modulation of the zero sequence and the modulation wave obtained by adding the three-phase output voltage values.

[0011] Further, the control of the first bridge arm, the second bridge arm or the third bridge arm comprises the following steps:

[0012] (11) obtaining the output phase voltage, the output inductance current and the bus voltage corresponding to the phase, and calculating the effective value of the phase voltage according to the output voltage and the bus voltage;

[0013] (12) calculating the difference between the effective value reference value of the corresponding phase and the effective value of the corresponding phase voltage, inputting the difference into a PI controller, multiplying the output value of the PI controller with the reference sine to obtain the reference value of the transient voltage loop of the corresponding phase;

[0014] (13) the difference between the reference value of the transient voltage loop and the output phase voltage is adjusted by a PR controller to obtain the reference value of the transient current loop;

[0015] (14) calculating the difference between the reference value of the transient current loop and the output inductance current, inputting the difference into a PI controller, and adding the injected third harmonic to the output value of the PI controller to obtain a modulation wave;

[0016] (15) the modulation wave is modulated by a PWM to obtain a PWM wave, and the first bridge arm, the second bridge arm or the third bridge arm is controlled by the PWM wave.

[0017] Further, the control of the fourth bridge arm includes the following steps:

[0018] (21) obtaining the voltage of the midpoint N of the two DC voltage division filter capacitors, the output phase voltage of the three-phase, the zero sequence current and the current of the filter inductance L n ;

[0019] (22) adjusting the difference between the voltage of the midpoint N and the third harmonic by a controller to obtain a first adjustment wave;

[0020] adjusting the difference between the average value of the output phase voltage of the three-phase and 0 by a controller to obtain a second adjustment wave;

[0021] multiplying the difference between the zero sequence current and the current of the filter inductance L n by the value of the impedance of the auxiliary network to obtain a third adjustment wave by a controller;

[0022] (23) summing the first adjustment wave, the second adjustment wave and the third adjustment wave to obtain a modulation wave, generating a triangular carrier signal by a SPWM modulation module, and controlling the fourth bridge arm by the triangular carrier signal.

[0023] Further, controlling the fourth bridge arm by the triangular carrier signal specifically includes: comparing the modulation wave with the triangular carrier signal, outputting a high level driving signal when the amplitude of the modulation wave is greater than the amplitude of the triangular carrier signal; outputting a low level driving signal when the amplitude of the modulation wave is less than the amplitude of the triangular carrier signal, and the power switching device T7 and the power switching device T8 of the fourth bridge arm are turned on and turned off according to the high level driving signal and the low level driving signal. The controller is a PI controller or a PR controller.

[0024] Beneficial effects: The present application has the following advantages over the prior art: the independent control of the first three bridge arms suppresses the negative sequence effect, the fourth bridge arm eliminates the zero sequence effect through the modulation of the third harmonic voltage, the modulation of the zero sequence current and the modulation wave obtained by adding the three-phase output voltage values, so that the three-phase four bridge arm inverter output realizes three-phase voltage balance under any load below the rated power. The control strategy of the traditional three-phase four bridge arm off-grid inverter needs a large number of coordinate transformation operations or the split capacitor capacity is too large, and the direct current utilization rate is low. Through the use of the sampled three-phase inverter output electrical signal, without any coordinate transformation, through the cooperative control of the first three bridge arms, the auxiliary network and the fourth bridge arm, each phase voltage is independently controlled, the stability of the system is improved, the calculation amount and complexity of the control strategy are reduced, the inverter output power quality and operating efficiency are improved, and strong support is provided for home and outdoor energy storage systems. Through separate control of each phase voltage, the control scheme is more clear and explicit, and a control framework is provided for related demand customization, so that the output waveform quality of the three-phase four bridge arm is higher, and the capacity of the split capacitor is reduced, the element volume is reduced, and the utilization rate of the direct current bus is improved. Strong engineering applicability, compared with the traditional method, without complex coordinate transformation, only the conventional sampling parameters need to be obtained, the algorithm calculation burden is small, easy to realize and industrialized production. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is the topology diagram of the three-phase four bridge arm inverter system in the application.

[0026] Figure 2 It is the principle diagram of the control process of the first three bridge arms of the three-phase four bridge arm inverter topology in the application.

[0027] Figure 3 It is the equivalent circuit of the fourth bridge arm and the auxiliary network of the three-phase four bridge arm inverter topology in the application.

[0028] Figure 4 It is the small signal control block diagram in the application.

[0029] Figure 5 It is the principle diagram of the control process of the fourth bridge arm of the three-phase four bridge arm inverter topology in the application.

[0030] Figure 6 It is the single-phase resistive load output current and voltage simulation diagram of the inverter in the application under extreme unbalance.

[0031] Figure 7 It is the single-phase inductive load output current and voltage simulation diagram of the inverter in the application under extreme unbalance.

[0032] Figure 8 It is the single-phase rectifying load output current and voltage simulation diagram of the inverter in the application under extreme unbalance.

[0033] Figure 9 The simulation diagram shows the output voltage and current waveforms of the three-phase inverter using the present invention under three different loads. Detailed Implementation

[0034] Example 1

[0035] like Figure 1 As shown, the three-phase four-arm inverter system based on stationary coordinate system control includes a two-level three-arm inverter, a fourth arm, an auxiliary network, a DC-DC converter module, and a control module. The two-level three-arm inverter includes three parallel arms and an output-side filter. The fourth arm is connected in parallel with the three parallel arms of the two-level three-arm inverter. The two-level three-arm inverter converts DC voltage into three-phase AC voltage and sends the three-phase AC parameters to the control module. The auxiliary network and the fourth arm primarily function to acquire zero-sequence current and harmonic current when the three-phase voltage is unbalanced. Based on the acquired three-phase electrical signals and bus voltage signals, the fourth arm is controlled according to the control signals to handle the effects of zero-sequence current and harmonic current, ensuring the balance of the three-phase voltage. The DC-DC converter module can be a Boost DC-DC converter, an uncontrolled rectifier, or a DC power supply device such as a battery pack.

[0036] The auxiliary network includes two DC voltage divider filter capacitors connected in series and a filter inductor L connecting the midpoint N of the two DC voltage divider filter capacitors. n Filter inductor L n The fourth bridge arm is connected to the midpoint of the bridge arm. Two series-connected DC voltage divider filter capacitors are connected in parallel with the four bridge arms. The midpoint N of the two DC voltage divider filter capacitors is connected to the output-side filter. The midpoints of the first, second, and third bridge arms are connected to the output-side filter. The control module includes a first control module and a second control module. The first control module controls the first, second, and third bridge arms based on the effective value loop of the phase voltage, the transient loop of the phase voltage, and the transient loop of the current. The second control module controls the fourth bridge arm based on the modulation wave obtained by the modulation of the third harmonic, the modulation of the zero sequence, and the sum of the three-phase output voltage values.

[0037] The first bridge arm includes power switches T1 and T2, the second bridge arm includes power switches T3 and T4, the third bridge arm includes power switches T5 and T6, and the fourth bridge arm includes power switches T7 and T8. The output-side filter includes a filter inductor L. a Filter inductor L b Filter inductor L c Filter capacitor C a Filter capacitor C b and filter capacitor C c Filter inductor La one end is connected to the midpoint of the power switch tube T1 and the power switch tube T2, and the filter inductor L a the other end is connected to the filter capacitor C a one end is connected to the A-phase load, and the filter inductor L c one end is connected to the power switch tube T3 and the power switch tube T4, and the filter inductor L c the other end is connected to the filter capacitor C b one end is connected to the B-phase load, and the filter inductor L c one end is connected to the power switch tube T5 and the power switch tube T6, and the filter inductor L c the other end is connected to the filter capacitor C c one end is connected to the C-phase load, and the filter capacitor C a , the filter capacitor C b and the filter capacitor C c the other end is connected to the midpoint N of the two DC voltage division filter capacitors, and the A-phase load, the B-phase load and the C-phase load are also connected to the midpoint N of the two DC voltage division filter capacitors.

[0038] The first control module comprises a first PI controller, a first PR controller, a second PI controller and a first PWM generator, the input of the first PI controller is the difference between the effective reference value of the phase voltage and the effective value of the phase output voltage, the input of the PR controller is the difference between the reference value of the phase transient voltage loop and the phase output voltage, the output of the PR controller is the reference value of the transient current loop, the reference value of the phase transient voltage loop is obtained by multiplying the output value of the first PI controller and the reference sine, the input of the second PI controller is the difference between the reference value of the transient current loop and the phase output inductor current, the input of the first PWM generator is the output of the second PI controller plus the injected third harmonic, and the PWM wave output by the first PWM generator is used for control of the first bridge arm, the second bridge arm or the third bridge arm.

[0039] The second control module comprises a second PR controller, a third PR controller, a fourth PR controller and a second PWM generator, the input of the second PR controller is the difference between the average value of the three-phase output voltage and 0, the input of the third PR controller is the difference between the voltage of the midpoint N and the third harmonic, the input of the fourth PR controller is the difference between the zero sequence current and the current of the filter inductor L n multiplied by the impedance of the auxiliary network, the input of the second PWM generator is the sum of the output values of the second PR controller, the third PR controller and the fourth PR controller, and the PWM wave output by the second PWM generator is used for control of the fourth bridge arm.

[0040] Embodiment 2

[0041] This embodiment provides a control method for the aforementioned three-phase four-arm inverter system based on stationary coordinate system control. The method includes individual control of each of the four arms. The control scheme is divided into two parts: the first part controls the first three arms, and the second part controls the fourth arm. Control of the first, second, and third arms is based on the effective value loop of the phase voltage, the transient loop of the phase voltage, and the transient loop of the current. Control of the fourth arm is based on the modulation of the third harmonic, the modulation of the zero sequence, and the modulation wave obtained by adding the three-phase output voltage values.

[0042] like Figure 2 As shown, the first bridge arm (power switches T1 and T2), the second bridge arm (power switches T3 and T4), and the third bridge arm (power switches T5 and T6) are controlled independently. This allows for independent control of the phase voltage of each phase. It is mainly divided into three loops: the effective value loop of the phase voltage, the transient loop of the phase voltage, and the transient loop of the current to ensure the output voltage value and waveform quality of each phase.

[0043] In a three-phase four-arm inverter system, the output phase voltages are respectively phase voltages U an U bn U cn Output phase current i a i b i c ; Filter inductor current i La i Lb i Lc Inductor current i in the auxiliary network Ln and bus voltage U dc And the voltage U at the midpoint N of the split capacitor in the auxiliary network. N The effective value U of the three-phase phase voltage is obtained through calculation. arms U brms U crms .

[0044] The control of each of the first three bridge arms is similar. Taking the first bridge arm connected to phase A as an example, the effective value reference value U of phase A is first set. anrmsref The effective value U of the output phase voltage of phase A arms The difference is fed into the PI controller, and the resulting output value of the PI controller is compared with the reference sine wave. Multiplying sinwt yields the reference value U of the transient voltage loop of phase A. * anrmsref Then set the reference value U * anrmsref With output phase voltage U an The difference is sent to the PR controller for adjustment to obtain the reference value I of the transient current loop. * anref , set the reference value I* anref The difference between the output inductance current i La and the output voltage is sent to a PI controller, and the output of the PI controller is added to the injected third harmonic and voltage feedforward U * aref U * ar , U * ar The PWM wave is obtained by comparing the triangle wave Trail* with the third harmonic, and the control method of the other two bridge arms controlled by the B and C phases is similar, so that the same control effect as the space vector control can be achieved.

[0045] The control of the fourth bridge, the traditional fourth bridge control method is to regard the zero sequence current generated by the unbalanced load as a disturbance of the fourth bridge arm, in the scheme proposed in the present embodiment, the zero sequence current is regarded as a current source, and the bus is regarded as a voltage source. According to the nature of the circuit, the influence on the midpoint potential of the split capacitor is realized by the bus voltage and the zero sequence current. That is, the midpoint potential of the split capacitor and the load neutral point are required to be consistent as much as possible, which is ensured by the circuit superposition principle. By controlling the fourth bridge arm, the midpoint potential of the split capacitor is modulated to be consistent with the injected third harmonic. Secondly, in order to ensure that the influence of the zero sequence current is minimized, that is, the zero sequence current is equal to the inductance current i Ln of the auxiliary network, the difference between the two is sent to a PR controller, and then multiplied by the impedance network composed of the auxiliary network to obtain the influence of the zero sequence current on the midpoint of the split capacitor. Finally, the modulation of the third harmonic and the modulation of the zero sequence are added, and finally the three-phase output voltage value is added as the modulation wave of the fourth bridge arm.

[0046] As shown in Figure 3 , the fourth bridge arm circuit adjusts the voltage of the midpoint potential of the split capacitor through the filter inductance of the power switch tube T7, T8 and the auxiliary network circuit. When T7 is turned on and T8 is turned off, the following can be obtained:

[0047]

[0048] When T7 is turned off and T8 is turned on, the following can be obtained:

[0049]

[0050] According to the switching period average model theory, the following can be obtained:

[0051]

[0052]

[0053]

[0054] wherein, is the duty cycle of the switching signal, is the equivalent capacitance, is the equivalent inductance, represents the Laplace operator.

[0055] According to equation (3), equation (4) and equation (5), combined with the Jelhoff law and the circuit superposition theorem, the small signal control block diagram of the fourth bridge arm circuit can be obtained as shown in Figure 4 .

[0056] According to Figure 4 the fourth bridge arm control block can be obtained as shown in Figure 5 , wherein since the first three bridge arms adopt the injection of third harmonic control, in order to process the third harmonic, the difference between the voltage U N of the midpoint N and the third harmonic is multiplied by the impedance of the auxiliary network, and then output V * 3Nnr The traditional split capacitor method is to ensure that the midpoint N is a fixed value to achieve the equal division of the split capacitor voltage. In order to ensure that the influence of the midpoint N potential on the split capacitor is reduced, the split capacitor value is required to be large. However, the midpoint N phase of the embodiment will dynamically change and adjust with the third harmonic, so the required capacitance value is relatively small. Then, the difference between the zero sequence current i n and the inductance current i Ln in the auxiliary network is multiplied by the impedance of the auxiliary network, and then output V * Lnr The sum of the three-phase inverter output phase voltages is divided by 3, and then subtracted from 0, and then sent to the PI or PR controller to output V * abcn The sum of V * 3Nnr , V * Lnr and V * abcn is obtained to obtain the modulation wave V * nr The modulation wave V * nr acts together with the triangular carrier signal Trail * to obtain the driving signal of the fourth bridge arm. The power switching devices T7 and T8 are turned on and off according to the driving signal of the fourth bridge arm.

[0057] The method based on the embodiment simulates various running conditions of different loads by Matlab / Simulink simulation software, such as Figure 6 Simulation diagram of single-phase resistive load at extreme imbalance, such as Figure 7 Simulation diagram of single-phase inductive load at extreme imbalance, such as Figure 8 Simulation diagram of single-phase rectifying load, and such as Figure 9 Simulation diagram of three-phase three different loads (A-phase rectifying load, B-phase resistive load, C-phase inductive load). It can be seen from the simulation diagram that the three-phase four-bridge inverter system can still ensure that the three-phase symmetrical voltage is quickly stable and can guarantee the stable amplitude and frequency of the output when the resistive, inductive and rectifying loads dynamically change in any combination after the control method proposed in the application.

Claims

1. A three-phase four-arm inverter system based on stationary coordinate system control, characterized in that, The system includes four parallel bridge arms, an auxiliary network, an output-side filter, and a control module. The auxiliary network includes two series-connected DC voltage divider filter capacitors and a filter inductor L connecting the midpoint N of the two DC voltage divider filter capacitors. n The filter inductor L n The control module is connected to the midpoint of the fourth bridge arm. Two series-connected DC voltage divider filter capacitors are connected in parallel with the four bridge arms. The midpoint N of the two DC voltage divider filter capacitors is connected to the output-side filter. The midpoints of the first, second, and third bridge arms are connected to the output-side filter. The control module includes a first control module and a second control module. The first control module controls the first, second, and third bridge arms based on the effective value loop of the phase voltage, the transient loop of the phase voltage, the transient loop of the inductor current, and the injected third harmonic loop. The second control module controls the fourth bridge arm based on the modulation wave obtained by the modulation of the third harmonic voltage, the modulation of the zero-sequence current, and the sum of the three-phase output voltage values. The first control module includes a first PI controller, a first PR controller, a second PI controller, and a first PWM generator. The input of the first PI controller is the difference between the effective reference value of the phase voltage and the effective value of the phase output voltage. The input of the first PR controller is the difference between the reference value of the phase transient voltage loop and the phase output voltage. The output of the first PR controller is the reference value of the transient current loop. The reference value of the phase transient voltage loop is obtained by multiplying the output value of the first PI controller by a reference sine wave. The input of the second PI controller is the difference between the reference value of the transient current loop and the phase output inductor current. The input of the first PWM generator is the output of the second PI controller plus the injected third harmonic. The PWM wave output by the first PWM generator is used for the control of the first bridge arm, the second bridge arm, or the third bridge arm. The second control module includes a second PR controller, a third PR controller, a fourth PR controller, and a second PWM generator. The input of the second PR controller is the difference between the average three-phase output voltage and 0. The input of the third PR controller is the difference between the voltage at the midpoint N and the third harmonic. The input of the fourth PR controller is the zero-sequence current and the filter inductor L. n The difference between the currents is multiplied by the impedance of the auxiliary network. The input of the second PWM generator is the sum of the output values ​​of the second PR controller, the third PR controller, and the fourth PR controller. The PWM wave output by the second PWM generator is used for the control of the fourth bridge arm.

2. The three-phase four-arm inverter system based on stationary coordinate system control according to claim 1, characterized in that, The first bridge arm includes power switches T1 and T2, the second bridge arm includes power switches T3 and T4, the third bridge arm includes power switches T5 and T6, the fourth bridge arm includes power switches T7 and T8, and the output-side filter includes a filter inductor L. a Filter inductor L b Filter inductor L c Filter capacitor C a Filter capacitor C b and filter capacitor C c Filter inductor L a One end is connected to the midpoint between power switch T1 and power switch T2, and the filter inductor L a The other end is connected to a filter capacitor C. a One end is connected to phase A load; filter inductor L c One end is connected to power switch transistors T3 and T4, and the filter inductor L c The other end is connected to a filter capacitor C. b One end and phase B load; filter inductor L c One end is connected to power switch transistors T5 and T6, and the filter inductor L c The other end is connected to a filter capacitor C. c One end is connected to the C-phase load, and the filter capacitor C is... a Filter capacitor C b and filter capacitor C c The other end is connected to the midpoint N of the two DC voltage divider filter capacitors. At the same time, the loads of phase A, phase B, and phase C are also connected to the midpoint N of the two DC voltage divider filter capacitors.

3. The three-phase four-arm inverter system based on stationary coordinate system control according to claim 2, characterized in that, It also includes DC-DC converter modules connected in parallel with the four bridge arms, which can be Boost DC-DC converters, uncontrolled rectifiers, or battery packs.

4. A control method for a three-phase four-arm inverter system based on stationary coordinate system control as described in any one of claims 1 to 3, characterized in that, This includes individual control of the four bridge arms; control of the first, second, and third bridge arms based on the effective value loop of phase voltage, the transient loop of phase voltage, and the transient loop of current; and control of the fourth bridge arm based on the modulation wave obtained by the modulation of the third harmonic, the modulation of zero sequence, and the sum of the three-phase output voltage values.

5. The control method according to claim 4, characterized in that, Control of the first arm, second arm, or third arm includes the following steps: (11) Obtain the output phase voltage, output inductor current and bus voltage of the corresponding phase, and calculate the effective value of the phase voltage based on the output voltage and bus voltage; (12) Calculate the difference between the effective value reference value of the corresponding phase and the effective value of the phase voltage of the corresponding phase, and input the difference into the PI controller. Multiply the output value of the PI controller with the reference sine to obtain the reference value of the transient voltage loop of the corresponding phase. (13) The difference between the reference value of the transient voltage loop and the output phase voltage is adjusted by the PR controller to obtain the reference value of the transient current loop; (14) Calculate the difference between the reference value of the transient current loop and the output inductor current, and input the difference into the PI controller. Add the injected third harmonic to the output value of the PI controller to obtain the modulated wave. (15) The modulation wave is obtained by PWM modulation, and the first bridge arm, the second bridge arm or the third bridge arm is controlled by the PWM wave.

6. The control method according to claim 5, characterized in that, Control of the fourth bridge arm includes the following steps: (21) Obtain the voltage at the midpoint N of the two DC voltage divider filter capacitors, the output phase voltage of the three phases, the zero-sequence current, and the filter inductance L. n The current; (22) The difference between the voltage at midpoint N and the third harmonic is adjusted by the controller to obtain the first regulating wave; The difference between the average value of the three-phase output phase voltage and 0 is used to adjust the second regulating wave through the controller; Zero-sequence current and filter inductor L n The difference in currents multiplied by the impedance of the auxiliary network is used to adjust the third regulating wave through the controller. (23) The first modulation wave, the second modulation wave and the third modulation wave are summed to obtain the modulation wave. The modulation wave generates a triangular carrier signal through the SPWM modulation module, and the fourth bridge arm is controlled by the triangular carrier signal.

7. The control method according to claim 6, characterized in that, The control of the fourth bridge arm via the triangular carrier signal specifically includes: comparing the modulated wave with the triangular carrier signal; when the amplitude of the modulated wave is greater than the amplitude of the triangular carrier signal, a high-level drive signal is output; when the amplitude of the modulated wave is less than the amplitude of the triangular carrier signal, a low-level drive signal is output; and the power switching devices T7 and T8 of the fourth bridge arm are turned on and off according to the high-level drive signal and the low-level drive signal.

8. The control method according to claim 7, characterized in that, The controller is a PI controller or a PR controller.

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